Hooking up Some sensors to a DAQ device

Discussion in 'The Projects Forum' started by AgedStudent, Jan 26, 2015.

  1. AgedStudent

    Thread Starter New Member

    Nov 24, 2013
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    I am doing a project using a modular NI DAQ chassis and want to make sure I am not missing anything obvious in regards to applying power.

    I have two sensors that need a 24V DC supply, a solenoid (24V DC) and another sensor that needs a 12V DC supply.

    I have a 24V DC power supply that I will connect to the +ve and com pins of an 8 channel digital output (DO) module.

    (This is the bit I want to check)

    I need to connect the solenoid to the (DO) device so that I can turn the supply on and off.

    I can connect the two 24V DC sensors directly to the power supply.

    I need a voltage regulator to bring the 24V DC supply down to 10V DC.

    My thinking is that I connect the system as shown below.

    upload_2015-1-26_22-47-57.png
    Is it that simple or am I missing something?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Well, you said 12V and drew 10V. And we can't tell if the DO is rated to handle 24V. Other than that, I don't see anything out of line. Your sensors might need cleaner power than the solenoid. So you should look at the specs of the power supply to see how well regulated that 24V is.
     
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  3. AgedStudent

    Thread Starter New Member

    Nov 24, 2013
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    Thanks for the quick reply!

    I need to regulate the voltage to 10V – 18V so 12V is fine.

    The DO is rated to 30V.

    The solenoid is controlling an air flow valve and is connected to the power supply via the DO module. The sensors are connected directly to the power supply. Why will the solenoid affect the power to the sensors?

    Anyhow, the power supply is well regulated at 24V.
     
  4. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Can you say which NI Module you are using? On the solenoid you will want to place a diode across the solenoid coil to act as a "flyback diode". Just keep in mind when the solonI am guessing the 10 volts is for a bridge type sensor circuit and acts as bridge excitation. Should that be the case you want a real stable 10 volts and I suggest using a chip like the Linear Technology LT 1031 or similar.
     
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  5. AgedStudent

    Thread Starter New Member

    Nov 24, 2013
    7
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    NI 9401 (DIO Module)
    NI PS-15 (Power Supply)

    You are spot on; the 10V is for a load cell with 700 ohm bridge resistance.
     
  6. AgedStudent

    Thread Starter New Member

    Nov 24, 2013
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    I have found a precision voltage regulator:

    http://www.ti.com/lit/ds/symlink/ref102.pdf

    upload_2015-1-27_14-57-21.png

    Do I leave the trim pin unconnected? Specs advise connecting pin 8 to ground with 1uF cap.

    Installation:

    upload_2015-1-27_14-58-8.png
    Are RL1 - RL3 representative of possible loads?
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Yes, although I was pointing out that a solenoid will operate on very noisy power whereas your sensors likely need nice smooth DC.

    Switching an inductive load - your solenoid - creates noise so that is an additional concern. Adding some isolation between the solenoid and the sensors is a good idea. Otherwise you might generate some feedback or oscillation problem.
     
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  8. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    I used several of those TI versions several years back and they worked fine, never needed the trim feature but it was there if needed.

    Ron
     
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  9. AgedStudent

    Thread Starter New Member

    Nov 24, 2013
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    0
    Thank you guys, you have been a great help.

    I will look into some isolation for the solenoid and I will upgrade my voltage divider - I suppose there's no point spending a couple of hundred on a sensor and then scrimping on the small stuff!

    Cheers

    Steve
     
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